Methods of RF sensing control and dynamic frequency selection control for cognitive radio based dynamic spectrum access network systems-cognitive dynamic frequency hopping

ABSTRACT

This invention relates to cognitive radio based wireless communications of dynamic spectrum access networks, and more particularly to a method of addressing radio frequency sensing control and dynamic frequency selection control. A method called Cognitive Dynamic Frequency Hopping that is based on the selective Simultaneous Sensing and Data Transmissions is described. The Cognitive Dynamic Frequency Hopping method is further facilitated by a collision avoidance technique. The described method satisfies both reliable and timely RF sensing for guaranteeing licensed user protection, and QoS satisfaction for services of the dynamic spectrum access systems.

RELATED APPLICATIONS

The present application relates to co-pending U.S. patent applicationSer. No. 11/549,895, filed on even date herewith, entitled, “METHODS OFMESSAGING CONTROL OF DYNAMIC FREQUENCY SELECTION (DFS) FOR COGNITIVERADIO BASED DYNAMIC SPECTRUM ACCESS NETWORK SYSTEMS” ; co-pending U.S.patent application Ser. No. 11/549,890, filed on even date herewith,entitled, “METHOD OF INTER-SYSTEM COEXISTENCE AND SPECTRUM SHARING FORDYNAMIC SPECTRUM ACCESS NETWORKS-ON-DEMAND SPECTRUM CONTENTION” ;co-pending U.S. patent application Ser. No. 11/549,906, filed on evendate herewith, entitled, “METHOD OF INTER-SYSTEM COMMUNICATIONS DYNAMICSPECTRUM ACCESS NETWORK SYSTEMS —LOGICAL CONTROL CONNECTIONS” ; andco-pending U.S. patent application Ser. No. 11/549,912, filed on evendate herewith, entitled, “ZERO DELAY FREQUENCY SWITCHING WITH DYNAMICFREQUENCY HOPPING FOR COGNITIVE RADIO BASED DYNAMIC SPECTRUM ACCESSNETWORK SYSTEMS”. These applications are incorporated herein byreference in entirety.

BACKGROUND OF THE INVENTION

The present invention relates to cognitive radio based wirelesscommunications of dynamic spectrum access networks, and moreparticularly to a method of addressing radio frequency sensing controland dynamic frequency selection control.

RF Spectrum scarcity, caused by costly spectrum access, becomes a majorissue for deploying future wireless communication systems, according tothe current spectrum allocation of regulatory organizations world wide.On the other hand, spectrum utilization measurements indicate thatfrequencies allocated in the licensed bands are largely under-utilized.For example, measurement shows that only 5.2% of spectrum is in use inthe US for the frequency bands below 3 GHz. Scarcity of spectrumlicensing and under-utilization of licensed bands motivate dynamicspectrum access that allows un-licensed wireless applications to operatein the licensed bands while insuring no harmful interference to theincumbent users in the licensed bands.

As an enabling technology for open spectrum access, cognitive radio isable to perform spectrum sensing, learning, and adapting to the RFenvironment so as to facilitate unlicensed radio operations andenhancement of spectrum reuse efficiency in intelligent ways. The keyissues are RF spectrum sensing, learning, and adaptation, withobjectives of guaranteeing incumbent service protection, and maintainingfair spectrum sharing and appropriate Quality-of-Service of cognitiveradio systems.

The charter of IEEE 802.22, the Working Group on Wireless Regional AreaNetworks (“WRANs”), under the PAR approved by the IEEE-SA StandardsBoard is to develop a standard for a cognitive radio-basedPHY/MAC/air-interface for use by license-exempt devices on anon-interfering basis in spectrum that is allocated to the TV BroadcastService.

This invention provides Medium Access Control (MAC) methods forCognitive Radio based dynamic access network systems, especially forIEEE 802.22 WRAN systems, addressing the key technical issues listedabove.

SUMMARY OF THE INVENTION

This invention relates to cognitive radio based wireless communicationsof dynamic spectrum access networks, and more particularly to a methodof addressing radio frequency sensing control and dynamic frequencyselection control. A method called Cognitive Dynamic Frequency Hoppingthat is based on the selective Simultaneous Sensing and DataTransmissions is described. The Cognitive Dynamic Frequency Hoppingmethod is further facilitated by a collision avoidance technique. Thedescribed method satisfies both reliable and timely RF sensing forguaranteeing licensed user protection, and Quality-of-Service QoSsatisfaction for services of the dynamic spectrum access systems.

A first embodiment is related to Simultaneous Sensing and DataTransmissions. This embodiment relates to cognitive radio based wirelesscommunications of dynamic spectrum access networks, and moreparticularly to a method of addressing radio frequency sensing controland dynamic frequency selection control. A wireless system, applying thedescribed method, uses the in-band channels for data transmissions andperforms channel sensing on out-of-band channels simultaneously. Thebands of spectrum and the number of channels for out-of-band sensing areselected adaptively by the system optimizing both sensing performanceand QoS of the system.

A second embodiment of the invention relates to Cognitive DynamicFrequency Hopping. This embodiment relates to cognitive radio basedwireless communications of dynamic spectrum access networks, and moreparticularly to a method of addressing radio frequency sensing controland dynamic frequency selection control. Based on the selectiveSimultaneous Sensing and Data Transmissions a wireless systemdynamically selects and switches operation frequencies (channels) fordata transmissions in continuous time periods. The frequency selectionis based on the simultaneous channel sensing performed along with datatransmissions.

A third embodiment relates to Collision Avoidance for Cognitive RadioDynamic Frequency Hopping. This embodiment relates to cognitive radiobased wireless communications of dynamic spectrum access networks, andmore particularly to a method of addressing radio frequency sensingcontrol and dynamic frequency selection control. A Cognitive RadioDynamic Frequency Hopping collision avoidance method that is based ondistributed coordination of wireless systems is described.

BRIEF DESCRIPTION OF THE DRAWINGS

The aforementioned and other features and objects of the presentinvention and the manner of attaining them will become more apparent andthe invention itself will be best understood by reference to thefollowing description of a preferred embodiment taken in conjunctionwith the accompanying drawings, wherein:

FIG. 1 is a baseline non-overlap RF sensing scheduling scheme;

FIG. 2 shows RF sensing on selective spectrum overlapping with datatransmissions;

FIG. 3 shows cognitive dynamic frequency hopping with simultaneousselective RF sensing;

FIG. 4 is an example of zero delay cognitive dynamic frequency hopping;

FIG. 5 shows cognitive dynamic frequency hopping collision caused byhidden nodes;

FIG. 6 illustrates collision avoidance for cognitive dynamic frequencyhopping;

FIG. 7 shows a DFH/CA algorithm;

FIG. 8 shows DFH/CA and simultaneous selective RF sensing on multiplechannels;

FIG. 9 shows a DFS messaging control mechanism;

FIG. 10 shows an on-demand spectrum contention algorithm;

FIG. 11 shows a coexistence scenario for 802.22 systems;

FIG. 12 shows an example of ODSC;

FIG. 13 shows a bridge CPE and coexistence connections;

FIG. 14 shows coexistence connections between two base stations;

FIG. 15 shows scheduling of service data transmissions and coexistenceoperations for a bridge CPE;

FIG. 16 shows an “over-the-backhaul” inter-system communicationsscenario; and

FIG. 17 shows a coexistence management entity in a protocol stack.

DETAILED DESCRIPTION

Cognitive Radio based Dynamic Spectrum Access Networks (DYSPAN),particularly IEEE 802.22 Wireless Regional Area Networks (WRAN) as anexample, provide the protection of licensed incumbent services throughfunctionalities such as RF spectrum sensing, dynamic frequency selection(DFS), and transmission power control (TPC).

RF sensing detects the channel occupancy of licensed incumbent servicesin the spectrum. DFS and TPC are mechanisms that dynamically adjust thetransmission frequency and the transmission power respectively of aDYSPAN (WRAN) system so as to avoid harmful interference to licensedincumbent services.

The Medium Access Control (MAC) layer of DYSPAN (WRAN) provides supportsfor RF spectrum sensing control, DFS control and TPC control in order toinsure the protection of licensed incumbent services while maintainingsatisfactory QoS.

RF sensing is the essential operation for licensed incumbent servicesprotection providing channel occupancy detection of licensed incumbentservices. Reliable RF sensing, however, might impact the datatransmission of a DYSPAN (WRAN) system due to the fact that RF sensingmay require interferences caused by data transmissions of its own systemto be below a certain threshold in order to guarantee reliable sensingperformance.

Based on the above observations, the objectives of the RF sensingcontrol scheme of the present invention are twofold: 1) RF sensing shallbe performed reliably and in a timely manner in order to guarantee theprotection of licensed incumbent services; and 2) The impact of RFsensing on data transmissions shall be limited to an acceptable levelsuch that the QoS requirements of DYSPAN (WRAN) systems can besatisfied.

There are two basic control approaches in which RF sensing can beperformed along with data transmission services: 1) Separated RF sensingand data transmission—RF sensing operations are performed inperiodically scheduled quiet sensing periods, in which no datatransmission service is allowed to be performed, and 2) Simultaneous RFsensing and data transmission—RF sensing and data transmissions areperformed in parallel.

In the first basic approach of RF sensing, every channel is sensed inperiodically scheduled quiet sensing periods, in which no datatransmission service is allowed to be performed. This solution option isreferred to as a “non-overlap” solution. The non-overlap solution hasthe advantage of reliable sensing performance because data transmissionsare ceased while sensing so that interference from the channel's ownsystem is zeroed. This solution, however, has two major drawbacks: 1)service interruption and 2) potentially low system utilization. Abaseline scheduling mode of the non-overlap solution 100 is shown inFIG. 1.

During a quiet sensing period 102, 110 data transmission services areceased until the end of the sensing period. The time of interruption isdictated by the sensing time which depends on both sensing technologyand licensed incumbent services. The interruption time becomes a part ofthe data transmission latency. In the case wherein the interruption time(quiet sensing time) is larger than a certain threshold, QoS of DYSPAN(802.22 WRAN) systems can not be maintained in terms of the transmissionlatency. Note that the maximum latency requirements are 20 ms for bothfull quality telephony and time critical packet, and 40 ms for standardquality telephony.

Moreover, no data transmission service is provided by the system duringa quiet sensing period 102. The system utilization for data transmissionservices, as shown in equation (1), is determined by the followingfactors: the quiet sensing time 102, the dynamic frequency selection(DFS) time 104, 106, 112, 114, 116 (DFS messaging time, DFS processingtime, etc.), and the period (inverse of frequency) of the RF sensing108.

$\begin{matrix}{{U_{Data} = {1 - \frac{T_{sensing} + T_{DFS}}{T_{{sensing}\_{perio}d}}}};} & (1)\end{matrix}$

In order to guarantee the licensed incumbent protection, the RF sensingperiod 108, T_(sensing) _(—) _(period), has to be less than or equal tothe Channel Detection Time 108 that is constrained by the licensedincumbent services. The DFS time 104, 106, 114, 116, T_(DFS), is acombination of the measurement reporting time, the report processingtime, and the channel closing time. Therefore the DFS time 104, 106,114, 116, depends on the efficiency of the DFS signaling algorithms anddecision-making algorithms. The aggregated DFS signaling (controlpackets exchange for DFS) time 104, 106, 114, 116, after a maximumallowed channel detection time 108 shall not exceed 100 ms according tothe requirement of incumbents in the IEEE 802.22 WRAN scenario. Asmentioned before, the time for reliable RF sensing 102, T_(sensing),sensing technology dependent and incumbent services dependent.

Given a stringent channel detection time 108 (RF sensing period) imposedby licensed incumbent services and imperfect sensing time 102 and DFStime 104, 106, the system utilization for data transmission servicescould potentially be below a level that is required for the acceptablenetwork throughput.

As for the second RF sensing control approach, Simultaneous Sensing andData Transmissions (SSDT), two control solutions can be conceived. Thefirst solution is to overlap data transmissions with RF sensing thatmonitors the full spectrum of channels including those that are in usefor data transmissions. This option is referred to as the “Full-SSDT”solution. Similarly, in the second option data transmissions areoverlapped with RF sensing, however, only those channels for whichreliable sensing can be achieved are monitored. This option is referredto as the “Selective-SSDT” solution.

With the “Full-SSDT” option, the system resolves problems of serviceinterruption and potential low system utilizations. Another advantage ofapplying the “Full-SSDT” option is that the system is also able torecord accurate timing (online) information with regard to channeloccupancy and vacancy of incumbent services so that more efficientspectrum utilization could be achieved. The major disadvantage of thissolution, however, is the self-interference to the sensing antenna whenthe channels in use are being sensed. It is difficult to achievereliable and timely RF sensing for guaranteeing incumbent protectionunless sophisticated sensing technologies for self-interferencemitigation are available, or reduced transmission power (which in turnaffects efficiency/throughput) is feasible.

According to the present invention, a Selective-SSDT solution is usedfor RF sensing control, which can overcome the drawbacks of the abovetwo solutions while maintaining their main advantages. As with theFull-SSDT solution, the method of the present invention allows a DYSPAN(WRAN) system to continuously perform data transmissions while operatingRF sensing such that service interruption and potential low systemutilization problems are resolved. In addition, instead of sensingchannels including the ones that are in use, a DYSPAN (WRAN) systemaccording to the present invention shall only sense the selectivechannels so that reliable and timely RF sensing can be substantiallyassured.

The Selective-SSDT solution of the present invention provides theflexibility of strategic and adaptive channel selections for RF sensing,with the above mentioned two options as two special cases—selecting nochannel and selecting all channels.

As depicted in FIG. 2, a DYSPAN (WRAN) system, applying theSelective-SSDT concept, uses the in-band channel(s) 206 for datatransmission and performs RF sensing on selective out-of-band channels202 and 210 simultaneously. Spectrum gaps 204 and 208 specify “guardbands” between the in-band channels (transmission spectrum) andout-of-band channels (sensing spectrum) in order to mitigate adjacentinterference caused by data transmission to the out-of-band channelsensing. The minimum width of the guard bands can be varied (takingeither positive or negative values) and depend on factors such as thesensing technology, the transmission power of the DYSPAN (WRAN) system,and the incumbent licensed services needed to be protected.

The bands of spectrum for RF sensing 202 and 210 shall be selectedadaptively by the DYSPAN (WRAN) system (specifically by the basestation) so as to provide the system the flexibility of optimizing bothRF sensing performance and QoS of the DYSPAN (WRAN) system. For example,a DYSPAN (WRAN) system should select a band of spectrum 202 and 210 fromwhich a significant number of vacated channels are most likely to befound, while reliable and timely RF sensing can be guaranteed.

The number of channels to be selected for RF sensing should also beadaptively adjustable. Sensing more channels can provide moreinformation regarding channel occupancy, which is desirable for DFSdecision-making. On the other hand, sensing more channels might requirelonger sensing time, more sensing reporting and report processing, whichmight negatively affect the QoS of the DYSPAN (WRAN) system. The basestation should make an intelligent decision for an optimal trade-off ofthese two factors, i.e. the sufficiency of channel information andQuality-of-Services.

A DFS control technique called cognitive Dynamic Frequency Hopping (DFH)according to the present invention is described below.

In order to satisfy the above-mentioned sensing control requirements,namely reliable and timely RF sensing guarantee and DYSPAN (WRAN) QoSsatisfaction, cognitive Dynamic Frequency Hopping (DFH) can be performedbased on the Selective Simultaneous Sensing and Data Transmissionconcept.

The Cognitive DFH technique that is based on Selective SimultaneousSensing and Data Transmissions (SSDT) according to the present inventionis described below.

As described above, the Selective-SSDT technique is a general andflexible solution for adaptive DFS decision-making. The selection of thesize of the guard band (as shown in FIG. 2) provides such generality andflexibility. An infinite positive guard band allows no simultaneoussensing or transmissions. A negative guard band allows simultaneoussensing and transmission on overlapped channels. A positive guard bandallows simultaneous sensing and transmission on non-overlapped channels.To simplify the description, when a positive guard band is used, in-bandchannels and out-of-band channels are not overlapped.

Operating in the Cognitive DFH mode, a DYSPAN (WRAN) system dynamicallyselects and switches operation frequencies (channels) for datatransmissions in continuous time periods. The frequency selection isbased on the simultaneous channel sensing performed along with datatransmissions. Both frequency selections and the length of an operationperiod in which a WRAN system operates on a channel should be determineddynamically in real time by a cognitive engine.

The DYSPAN (WRAN) operations applying Cognitive DFH technique areillustrated in FIG. 3. Note that although the case wherein the DYSPAN(WRAN) system operates on a SINGLE channel is shown in FIG. 3, thetechnique of the present invention can be applied to MULTIPLE channelcases without losing generality, as is described in further detailbelow.

The DYSPAN (WRAN) operations in DFH mode are carried out in continuousoperation periods referred to as DFH Operation Periods, that havevariable lengths. Except the Initial Sensing period 302 (at the verybeginning of the DYSPAN /WRAN operation for channel availability check),a DYSPAN (WRAN) system performs both data transmissions on a channel,say Channel A, and RF sensing on channels [0, A-n] and channels [A+n, N]in each operation period 304. Here Channel “0” and Channel “N” arereferred to as the lower bound and upper bound of the sensing spectrumrespectively and “n” is the number of channels in the guard band. Inparallel with data transmissions the next channel to hop for datatransmissions is selected. At the end of a DFH operation period, theWRAN system hops to the selected channel and starts the next DFHoperation period.

The validation time of a channel is defined as the latest time at whichthe channel is validated to be vacant as indicated by measurementresults of the RF spectrum sensing, and should be the end of the sensingduration for that channel. The grace period is defined to be the maximumperiod of time in which a licensed incumbent service can tolerateinterference generated by licensed exempt (DYSPAN/WRAN) systems,starting from the beginning of the licensed incumbent service'soperations, and is equivalent to the Channel Detection Time for theincumbent.

After hopping to a new channel, a DYSPAN (WRAN) system performs datatransmission on that channel for a Cognitive DFH Operation Period 304 or306. The length of a DFH operation period can be varied for a particularchannel. The length of a DFH operation period shall not exceed the timeperiod in which it is guaranteed that the DYSPAN (WRAN) operations onsuch channel do not cause any harmful interference to any licensedincumbent service. In other words, for a channel, say channel A, that isin use for data transmissions, the Cognitive DFH operation period ofchannel A shall be terminated before the validation time of channel Aplus the length of a grace period (i.e. the Channel Detection Time),considering the worst case scenario that a licensed incumbent serviceappears immediately after the validation time of channel A.

The DFH operations of a DYSPAN (WRAN) system during a Cognitive DFHoperation period are specified as follows:

1) The base station schedules the whole system (the base station and allthe associated customer devices/CPEs) to hop (switch) to a channel, saychannel A, based on the frequency selection decision made at the end ofthe previous operation period.

2) The base station and all CPEs in the system perform datatransmissions on channel A 304;

3) The base station performs and schedules all CPEs to perform RFsensing on channels [0, A−n] and channels [A+n, N] simultaneously withdata transmissions 304;

4) CPEs report sensing measurement results to the base station;

5) The base station processes sensing measurement reports;

6) The base station performs channel selections, and channelacquisitions when it is necessary;

7) The base station announces the frequency selection decision to beused for the next operation period to all CPEs in the system and to allneighbor DYSPAN (WRAN) systems.

8) Go to Step 1) for the next DFH Operation Period.

Channel setup and maintenance procedures that guarantee zero(negligible) frequency switching delay for cognitive DFH are nowdescribed.

Frequency switching overheads when a DYSPAN (WRAN) system switches tonew frequency are considered. A novel channel setup and maintenancemechanism that guarantees frequency switching with zero (negligible)delay for cognitive DFH is presented.

Before switching to a new channel, a channel availability check has tobe performed in order to ensure the channel availability (incumbentfree). Also, the channel availability timing requirement has to besatisfied. In the WRAN scenario, the channel availability check time is30 seconds.

Channel setup is to set up operation parameters for reliablecommunications on a selected new channel. Operations of channel setupmay include initial channel ranging between the base station and CPEs,and all other operations that are required to setup operation parametersfor reliable communications on a selected channel.

In the WRAN scenario, the channel setup time may take up to 2 seconds,in which the integrated channel open transmission time is up to 100 ms.

The overhead for channel setup is required to initiate reliablecommunications on a new channel or a channel that is not effectivelymaintained.

Channel Move Messaging and Hardware Switching Time are also consideredas frequency switch overhead and should be considered in the overhead offrequency switching to a new channel.

Once the transmission parameters have been setup for reliablecommunications on a channel, regular or periodic channel maintenancesshall be performed by the DYSPAN (WRAN) systems to adjust thetransmission parameters adapted to the dynamic channel conditions.Regular channel maintenance includes operations such as regular/periodicchannel ranging.

Specified below is a channel setup and maintenance mechanism thatguarantees zero (negligible) delay frequency switching according to thepresent invention (referring to FIG. 4):

-   -   1. Select and maintain a cluster of channels that have passed        the Channel Availability Check 408, 418, 428. This channel        cluster is referred to as Cluster A.    -   2. Perform (initial) channel setup 410, 420, 430 for new        channels in Cluster A. Channels in Cluster A for which channel        setup has been performed successfully are referred to as        channels in Cluster B. Note that a channel that is not        effectively maintained through regular channel maintenance is        considered as a new channel.    -   3. Perform Cognitive Dynamic Frequency Hopping among channels in        Cluster B.    -   4. Perform regular/periodic channel maintenance for the        operation channel on which the DYSPSN (WRAN) is performing data        transmissions.    -   5. The DYSPAN (WRAN) system shall schedule Cognitive Dynamic        Frequency Hopping such that the maximum interval of regular        (periodic) channel maintenances for all CPEs on every channel in        Cluster B is not exceeded. The maximum maintenance interval for        each CPE is to guarantee the effectiveness of transmission        parameters obtained from the previous channel maintenance. A        channel is identified as well-maintained if the above condition        (maintenance interval less than the maximum allowed interval) is        satisfied.    -   6. If a channel is not well-maintained, the DYSPAN (WRAN) system        shall eliminate this channel from Cluster B.    -   7. Channel Move information is embedded in the MAC management        messages that are regularly transmitted from the base station to        CPEs. So the delay for channel move messaging is negligible.    -   8. The delay for Hardware Switching Time is considered to be        negligible.

The mechanism described above combines regular (periodic) channelmaintenance with cognitive dynamic frequency hopping over a cluster ofvacated channels that are initially setup such that the channel set updelay for channel switching is eliminated.

The typical maximum maintenance interval for Wireless Broadband AccessNetworks (e.g. IEEE 802.16 WiMAX) is about 30 to 35 seconds.

FIG. 4 provides an example of Zero-overhead cognitive (dynamic)frequency hopping. Initially, Channel Availability Checks 408, 418, 428are performed on Channel X, Y, and Z 402, 404, 406. After passingChannel Availability Check on for example channel X 402, the system 400performs Channel Setup 410 on channel X 402, while continuing ChannelAvailability Checks on Channel Y and Z 404, 406. After having completedChannel Setup 410 on Channel X 402, the system 400 switches to channel Y404, which has passed the channel availability check 418, and performsChannel Setup 420 on Channel Y 404, while performing channel sensing 412on Channel X 402 and Channel Availability Check 428 on Channel Z 406.Similarly, the system switches to Channel Z 406 and performs ChannelSetup 430 on Channel Z 406 after having completed channel setup 420 onChannel Y 404, while simultaneous channel sensing 412, 422 are performedon both Channel X 402 and Channel Y 404. Insuring an incumbent-freecondition on Channel X 402 through channel sensing 412, the system 400switches to channel X 402 and performs data transmissions and channelmaintenance 414, with simultaneous channel sensing 422 and 432 onchannel Y 404 and channel Z 406. Similarly, the system 400 switches tochannel Y 404 or channel Z 406 and performs data transmissions andchannel maintenances 424, 434 while simultaneous channel sensing 416,426, 432 are performed. If an incumbent has been detected during thechannel sensing period 416 of channel X 402 (as an example), the system400 shall avoid using channel X 402 for at least a period of ChannelNon-occupancy Time. In such condition, the system 400 continuesCognitive DFH operations 436, 438 on channel Y 404 and channel Z 406.

A cluster of vacated channels is maintained in order to enable:

-   -   Zero-overhead channel switching.    -   Flexible channel management for multiple DYSPAN (WRAN) systems.

Collision Avoidance for Frequency Switching is now described. Therepotentially exists a “hidden node” problem that would cause two neighborDYSPAN (WRAN) systems to collide on channel use. Two neighbor DYSPAN(WRAN) systems might independently select the same frequency to switchto for their next operation periods. Their frequency switching mighthave taken place before they are able to detect such a conflictingsituation. In such a case, collision occurs if these two systems caninterfere with each other.

FIG. 5 depicts the “hidden node” problem 500 and the consequentcollision of frequency use when DFH is applied. Two neighbor systems Aand B, 502 and 504, both detect that channel C is valid and thevalidation times of channel C for these two systems are relativelyclose. Assume that system A and B both independently decide to selectchannel C to be used in their next DFH operation periods which areoverlapped with each other. If both system A and B hop to channel Capproximately at the same time in their overlapped DFH operationperiods, collision 510 on channel C occurs. The occurrence of thechannel-use collision is due to the fact that a system has no knowledgeabout the frequency selected by its neighbors for the future use in anoverlapped operation period, and such channel-use information can onlybe detected when a potential colliding channel is actually in use.

To avoid frequency hopping collision, the present invention introduces atechnique called DFH/CA (collision avoidance), as is illustrated inFIGS. 6 and 7. Note that such a collision avoidance technique is generalenough to be applicable to general frequency switching.

FIG. 6 illustrates collision avoidance for cognitive (dynamic) frequencyhopping 600 for a System A 602 and a System B 604. System A 602 andsystem B 604 are all working in DFH mode (606, 608, 612, 614). AfterSystem B selects channel C for the next hopping period, it announcessuch decision to all neighbors —System A in this example —before hoppingto channel C. System B then waits for responses from its neighbors, andhops to channel C if no responses are received. System A monitors andreceives DFH announcement messages. When a DFH announcement (indicatingchannel C will be in used by System B) is received, System C selects adifferent channel —channel B —hence a collision can be eliminated(collision free 610).

A collision-avoidance algorithm 700 for Cognitive DFH is shown in FIG.7. After a DYSPAN (WRAN) system has selected a frequency as the nexthopping frequency 704, it shall announce this DFH decision to allneighbor DYSPAN (WRAN) systems 706 and wait for a reasonable amount oftime 708 (round trip time at minimum) before hopping to the selectedfrequency. All DYSPAN (WRAN) systems shall monitor the DFH announcementsfrom neighbor systems at all times. A DYSPAN (WRAN) system that isannouncing a COGNITIVE DFH decision can hop to the selected frequency716 when the waiting period is expired 710, only if the system does notreceive another COGNITIVE DFH announcement from any neighbor thatselects the same frequency 712. The waiting period is to account for thesituation in which a neighbor system transmits the same announcementbefore receiving the COGNITIVE DFH announcement, and the minimum waitingperiod should be a round trip propagation delay between two neighborsystems.

When receiving a COGNITIVE DFH announcement, a DYSPAN (WRAN) systemshould react in one of the following three ways under the appropriateconditions. If a DYSPAN (WRAN) system receives a COGNITIVE DFHannouncement without having simultaneously announced the same frequencyselection, it shall not hop to the frequency selected by the receivedannouncement in the next operation period. On the other hand, if thereceived COGNITIVE DFH announcement has the same frequency selection asthe DYSPAN (WRAN) system has just announced, and if the time stamp ofits own announcement is earlier than the time stamp of the received one714, the DYSPAN (WRAN) system can hop to the selected frequency in thenext operation period after the waiting period is expired. Otherwise, ifthe time stamp of its own announcement is equal to or later than thetime stamp of the received announcement for the same frequencyselection, the DYSPAN (WRAN) system shall not hop to the selected(conflicting) frequency in the next operation period.

Although the above description assumes that the DYSPAN (WRAN) systemoperates on a single channel, the technique of cognitive dynamicfrequency hopping (with collision avoidance) with simultaneous selectivesensing can be naturally extended to DYSPAN (WRAN) systems that operateon multiple channels.

A relatively simple extension of the COGNITIVE DFH/CA+Selective Sensingtechnique to multiple channels is to treat a single channel in the abovedescription as a set of channels that have the same validation times.This assumption is realistic if it is feasible that a set of contiguouschannels can be sensed and validated all at once.

For a more general case, FIG. 8 shows how the COGNITIVE DFH/CA with thesimultaneous selective sensing technique is applied to a DYSPAN (WRAN)system that operates on two channels in parallel. In this case, theDYSPAN (WRAN) system (the base station) shall record the validation timeof each channel that is in use in order to guarantee the operationperiod of each operating channel does not exceed the limit constrainedby the grace period of licensed incumbent services. Specifically, theinterval between the validation time of channel A and the terminationtime of the Operation Period of Channel A 804 shall be less than theGrace Period. In parallel with operation on channel A, the systems canoperate on channel B insuring that the interval between the validationtime of channel B and the termination time of the Operation Period ofChannel B 802 shall be less than the Grace Period. Similarly operationon channel C 806 can be performed in parallel with operation on channelB 802 following the same rule as described above.

An overview of DFS messaging control is now described. DFS messaging isa mechanism of exchanging control packets between the base station andCPEs in order for DFS decision-making and DFS assignment. Informationexchanged through DFS messaging include reporting schedules, RF sensingreports, DFS assignments, and other related signaling messages. Alongwith RF sensing, DFS messaging is performed simultaneously with datatransmissions. The advantage of such parallel operations is thatsufficient time for RF sensing and DFS messaging is guaranteed withoutaffecting QoS of the data transmission services such as latency andthroughput. The DFS messaging control algorithm 900 is shown in thefollowing flow chart in FIG. 9.

A DYSPAN (WRAN) system starts the operations with initial RF sensing 904that searches for available frequencies for the data transmissionservices (channel availability check). The base station then announcesthe DFS decision 906 based on the RF sensing results to both CPEs in thesystem and the base stations of neighbor systems. The DYSPAN (WRAN)system will then hop to the selected frequency if the DFS decision iseffective and start data transmissions. Simultaneously with datatransmissions, the Selective RF sensing 908 is continuously performed onfrequencies for which reliable sensing performance can be achieved.

The base station shall schedule measurement reporting 910 of all CPEsafter reliable RF sensing by CPEs have completed. The goal of the reportscheduling 910 is to facilitate reliable, efficient and flexiblemeasurement reporting. All CPEs shall report their RF sensing results912 in accordance with the report scheduling.

The base station will acknowledge the successful measurement reports andre-schedule 918 the unsuccessful measurement reports until all CPEs havereported successfully 914 or the maximum number of scheduling retrieshas been exceeded for the unsuccessful reporting 916. After that thebase station processes and summarizes the RF sensing reports of thewhole system (information from neighbor systems and database of theservice provider shall also be included). The base station then selectsthe best frequencies to be used in the next DFH operation period andmakes announcements to all CPEs in the system and to all neighborsystems (base stations) regarding its DFS decision 906. Finally, afteradjustments on the DFS decision according to the feedbacks from the CPEsand the neighbor systems to the DFS announcement 906, the base stationassigns the new frequency selected to the CPEs for use in the nextfrequency hopping period.

The RF sensing report 912 is now described. The base station and CPEsshall be able to detect at least four channel conditions as follows:

-   -   Licensed incumbent service occupied    -   Another DYSPAN (802.22 WRAN) system occupied    -   Noisy    -   Vacant

Bit-vector reporting is now described. CPEs shall have signal processingcapabilities to estimate and identify these channel conditions. Insteadof including the raw measurement data in the measurement reports, CPEsreport the channel conditions using a simple bit vector. Two bits perchannel is sufficient to represent the channel condition in themeasurement reports for the above four possible conditions.

On-request raw-data reporting is now described. The base station shallalso be able to request the CPEs to report the raw data of the sensingmeasurement. Although this method requires more bandwidth fortransmitting sensing reports, it enables advanced data analysis to beperformed on the raw data of the sensing measurement that would only befeasible in the base station.

Combining the bit-vector reporting and the on-request raw-datareporting, a DYSPAN (WRAN) system can achieve a balance betweenefficiency of report transmission and accuracy of data analysis.

The validation time for each non-incumbent-occupied channel shall beincluded in the measurement report.

Scheduling of measurement report 910 and measurement reporttransmissions 912 are now described. The measurement reports shall betransmitted in the scheduled transmission opportunities from CPEs to thebase station (uplink transmissions). The goal of the measurement reportscheduling is to facilitate reliable, efficient and flexible measurementreporting. Three scheduling methods are feasible: polling, “poll-me”,and contention.

In the polling method, the base station polls CPEs to transmitmeasurement reports by scheduling transmission opportunities forreporting in the up-link MAP. When being polled, a CPE should transmitthe measurement report if one is ready. Otherwise a CPE should eitherreturn feedback information or other useful data to the base station ifpossible. The base station should provide redundant report transmissionopportunities for each CPE in order to enhance the report transmissionreliability. In case the report transmission opportunities are ignoredby a CPE, the wasted bandwidth (polling overhead) is negligible giventhe allocated bandwidth for transmitting a bit-vector report is usuallynegligibly small. The base station should also poll a CPE only when themeasurement report is likely to be ready in order to reduce pollingoverhead.

In the “Poll-me” method a CPE can request bandwidth allocation for thereport transmission by using a 1-bit “poll-me-for-reporting” flag in theBandwidth Request packet data unit (PDU)

In the Contention method, the base station shall schedule or providecontention-base transmission opportunities for report transmissions.CPEs shall send polling requests or transmit measurement reports throughthe contention transmission opportunities for time-critical reportingsituations.

Report re-scheduling and acknowledgement 918 is now described. The basestation shall re-schedule CPEs that have been scheduled (polled) butwhose measurement reports have not been successfully received by thebase station. The re-scheduling is through report transmission pollingas described above in a subsequent up-link MAP.

The base station implicitly acknowledges measurement reports that it hassuccessfully received. This is done by ignoring report re-scheduling forCPEs from which reports have been successfully received. In other words,if a CPE, which has been polled and has transmitted a measurement reportin a previous frame, is not re-polled in the subsequent up-link MAP, theCPE shall regard that its report has been successfully received by thebase station.

DFS Decision-making, Announcement, and Adjustment 906 is now described.After collecting and processing measurement reports received from CPEs,the base station selects the valid channels to use for the system in thenext cognitive DFH operation period. If the measurement reports arerepresented using bit-vector format, DFS decisions could be made by thebase station using simple logic ORs. The DFS decision shall be announcedto all CPEs in the system before the selected frequency is assigned tobe used in the next cognitive DFH operation period. The DFS announcementshall be made early enough so that CPEs can return feedbacks regarding adefective DFS decision before the current COGNITIVE DFH operation periodterminates. The base station shall adjust a defective DFS decision if itis indicated by feedbacks from CPEs. The DFS decision shall be announcedto all neighbor systems to prevent colliding DFS decisions amongneighbor systems.

In addition to avoidance of harmful interference to licensed incumbentservices as the first priority, a DYSPAN (WRAN) system shall coexistwith other DYSPAN (WRAN) systems by sharing the spectrum holes (spectrumunused by licensed incumbent services).

The objective of DYSPAN (WRAN) system coexistence and spectrum holesharing is to provide fair, efficient, and adaptive spectrum accessesfor DYSPAN (WRAN) systems. A spectrum sharing mechanism according to thepresent invention is called On-Demand Spectrum Contention, whichintegrates DFS and TPC with spectrum contentions and provides fairness,efficiency, and adaptability of spectrum access using activeinter-system coordination.

Since the coordinative coexistence mechanism is favorable for fairness,efficiency and adaptability, it becomes very critical to provideefficient methods for inter-system communications in order to guaranteethe feasibility and the overall efficiency of the coexistence (spectrumsharing) mechanism. A method called Logical Control Connections forinter-system coordination is described according to the presentinvention, which can be established and maintained both over-the-air andover-the-backhaul with very low communication overhead incurred.

In the following two subsections, the On-Demand Spectrum Contention(ODSC) spectrum sharing mechanism and the inter-system communicationsmethod using Logical Control Connections (LCC) are both described indetail.

The Spectrum sharing mechanism called On-Demand Spectrum Contention(ODSC) according to the present invention is now described. FIG. 10illustrates the ODSC algorithm 1000.

Starting with system initializations 1010, a ready-to-operate DYSPAN(WRAN) system first performs channel evaluations and channel selections1012 to detect spectrum holes. Note that the licensed incumbent serviceprotection is an essential and integrated component of the DYSPAN(802.22 WRAN) co-existence mechanism being described here. Operations ofchannel evaluation and selection include RF sensing, measurementevaluations, measurement reporting, report processing and frequencyselection, which are proposed and described in detail in the “LicensedIncumbent Service Protection” section.

Then the DYSPAN (WRAN) system verifies whether non-exclusive sharing ofthe selected channels is feasible 1014. Non-exclusive sharing of aselected channel is to share the selected channel through transmissionpower control (TPC) such that DYSPAN (WRAN) systems sharing the samechannel do not cause harmful interference to one another. Anon-exclusive spectrum sharing method is feasible as long as the maximumachievable signal-to-interference-ratio (SIR) on the selected channel ishigher than the required SIR of the DYSPAN (WRAN) for the supportedservices.

If non-exclusive sharing of the selected channels is feasible, theDYSPAN (WRAN) system then makes a DFS decision and schedules datatransmissions on the selected channels with appropriate TPC settings1024. DFS announcing and DFH/CA take place before data transmissions areperformed on the selected channels.

On the other hand, if non-exclusive sharing is unfeasible, exclusivesharing of the selected channels shall be performed. The exclusivechannel sharing problem is resolved through spectrum contentions 1018which are facilitated by inter-system coordination. It is assumed thatthe same type of DYSPAN (802.22 WRAN) systems can only effectivelycommunicate with one another for coordination of spectrum sharing of theselected spectrum hole —such a simple assumption can be extended so thatdifferent type of DYSPAN systems can effectively communicate forspectrum sharing coordination (for example, 802.22 WRAN and 802.16 WiMAXsystems).

Based on the above assumption, if the selected channel (spectrum hole)is not occupied by a specific type of DYSPAN (e.g. 802.22 WRAN) system1016, the DYSPAN (802.22 WRAN) system has to give up the effort ofspectrum sharing on the selected channel and performs data transmissionswithout using the selected channels if it is possible 1026. Otherwise,the DYSPAN (WRAN) system should initiate the spectrum contention process1018 for the ownership of the selected channels with the DYSPAN (WRAN)system of the same type that is occupying the spectrum.

The basic components of the spectrum contention process 1018 includeContention request, Contention resolution, and Contention response. Thespectrum contention process includes a contention request function inwhich a requesting system generates and transmits contention requestscontaining contention tokens that are received by a responding system.The spectrum contention process includes a contention resolutionfunction in which spectrum contentions are resolved in a respondingsystem by comparing the contention tokens generated by the contendingsystems.

If the contention succeeds 1020, the DYSPAN (WRAN) system acquiring theselected channel makes a DFS decision and schedules data transmissionson the selected channels 1024 starting from the time agreed upon by bothcontending systems (a grace period is described in further detailbelow). DFS announcing and DFH/CA shall take place before datatransmissions are performed on the acquired channels.

If the contention fails, the DYSPAN (WRAN) performs data transmissionswithout using the selected channels if it is possible 1026. The DYSPAN(WRAN) system that is occupying the selected channel shall release thechannel (stop scheduling data transmissions) at the time (after adefined grace period) agreed upon by both contending systems.

In the data transmissions state 1022 of a DYSPAN (WRAN) system, as shownin FIG. 9, two types of demands can initiate an iteration of thespectrum sharing process 1000. These are internal demands and externaldemands.

Internal demands are generated by a DYSPAN (WRAN) system itself and arethe consequences of the channel condition and workload conditionanalysis performed by the DYSPAN (WRAN) system. For example, when thecurrent channel condition is not able to support the QoS of the givenadmitted service workloads, an internal demand is generated andinitiates an iteration of the full spectrum sharing process 1000 so thata better channel or more channels can be acquired to satisfy the QoSrequirements of the given workloads.

External demands are coexistence requests received from other DYSPAN(802.22 WRAN) systems. When an external demand is received, a DYSPAN(WRAN) system shall initiate spectrum contention iteration 1000.

The ODSC mechanism 1000 using a coexistence scenario example 1100 isdepicted in FIGS. 11 and 12.

In this coexistence scenario, DYSPAN (WRAN) system 3 1112 has overlappedmaximum coverage areas with both DYSPAN (WRAN) system 1 1110 and DYSPAN(WRAN) system 2 1114, but the maximum coverage areas of system 1 1110and system 2 1114 do not overlap. Assume harmful interference exists inthe overlapped coverage areas if both systems operate on the samefrequency simultaneously. So DYSPAN (WRAN) system 3 1112 needs tocoexist with both system 1 1110 and system 2 1114. As shown in FIG. 11,inter-system communications for coexistence are via Logical ControlConnections (LCC) 1116 which allows simultaneous coexistencecommunications and data transmissions. LCC will be described in detailin the following section.

FIG. 12 shows an example of ODSC 1200 among systems in the abovescenario 1100. Initially system 1 and system 2 are both operating onchannel “a” for data transmissions simultaneously 1201, 1204, and system3 just starts its operation and does not occupy any channel. Internaldemands of system 3 for bandwidth to support data services initiatesystem 3 to perform spectrum acquisition 1000.

The channel evaluation process 1012 indicates that channel “a” is theonly channel that is not occupied by any licensed incumbent service insystem 3's coverage area. System 3 then selects channel “a” as acandidate for data transmissions. Meanwhile, system 3 also detects thatchannel “a” is occupied by both system 1 and system 2, and non-exclusivesharing of channel “a” is not feasible.

System 3 generates and sends spectrum contention requests 1208 to bothsystem 1 and system 2 contending for channel “a”. After receiving thecontention request 1208 from system 3 as an external demand, both system1 and system 2 initiate their spectrum contention process 1000 and thenreturn system 3 a contention response message 1209 respectivelyindicating contention results. In case of losing the contention, whichis the case for system 1 and system 2, a DYSPAN (WRAN) system shallinclude in the contention response message 1209 the time at which theoccupied channel will be released (channel release time). The channelrelease time shall not be immediately after the time of contentionresolution and a DYSPAN (WRAN) shall be allowed to continue the datatransmission on the lost channel for up to a maximum grace period 1206before the lost channel is released (as shown in FIG. 12).

After winning channel “a” 1020 from both system 1 and system 2, system 3shall announce the DFS decision of using channel “a” and schedule datatransmission services on channel “a” 1203, 1024 starting from anappropriate time which is a summary of the channel release timesreceived from the other two systems.

On the other hand, after losing a channel 1020 (channel conditionchange) a DYSPAN (WRAN) system should perform another iteration of ODSCoperations 1000 initiated by internal demands in order to acquiresufficient bandwidth to maintain the on-going data transmission servicesbefore the just lost channel is released. In this example, system 1 andsystem 2 acquire channel “b” 1202 and channel “c” 1205 respectivelybefore channel “a” is released.

The properties of the ODSC mechanism in this section are characterizedin terms of efficiency, adaptation and fairness. Efficiency includes lowoverhead and low complexity.

Coexistence overheads are only incurred when there are either internalor external demands. There is no constant coexistence overhead that isnecessary. Coexistence overheads include communications and computationsincurred for coexistence. Particularly, communications for coexistenceare through very low overhead logical control connections 1116(described later), which allow overlapping of coexistence communicationswith data transmission services 1200. Only a simple contention mechanism1000 is required to coordinate multiple DYSPAN (WRAN) systems forcoexistence purposes. No complicated mechanism for spectrum negotiation,allocation or scheduling is needed. Decision-making (contentionresolutions) for spectrum sharing is distributed to be performed inindividual systems. This provides the advantage of scalability comparedto centralized approaches.

The ODSC mechanism of the present invention is highly adaptive to bothinternal demands and external demands for inter-system coexistence andradio resource management, which are usually interleaved together, inreal time. The internal demands include RF channel conditions andworkload conditions (rate/QoS requirements). Dynamic channelevaluations/selections 1012 and spectrum sharing/contentions 1018 areinitiated adapting to internal demands. The external demands includecoexistence (spectrum contention) requests from neighbor DYSPAN (WRAN)systems. Spectrum contentions 1018 can be directly initiated respondingto the external demands.

The ODSC mechanism of the present invention can provide bothlocal/short-term and global/long-term fairness for spectrum accesses.The ODSC mechanism resolves exclusive-sharing of spectrum holes throughthe contention-based solution that provides fair spectrum accesses(equal right to access the RF spectrum) for every DYSPAN (WRAN) systemat any time. The ODSC mechanism is an iterative process that can beinitiated by either internal or external demands adapting to variousworkload and environment conditions. Such an iterative process ofadaptive spectrum contention can lead to long term global(multi-systems) fairness.

In summary, the ODSC mechanism of the present invention provides anefficient, self-organized, adaptive and fair framework for coexistenceand (inter-system) radio resource management of DYSPAN (802.22 WRAN)systems.

As mentioned in the previous sections, inter-system communications arerequired for collaborative coexistence of DYSPAN (802.22 WRAN) systems,and the development of efficient methods for inter-system communicationsis critical to guarantee the feasibility and overall efficiency of thecollaborative coexistence mechanism. A communications method calledLogical Control Connections for the inter-system coordination accordingto the present invention is described, which can be established andmaintained both over the air and over the backhaul with very lowcommunications overhead incurred in terms of spectrum bandwidth,messaging latency, and hardware/software complexities.

An Over-the-air Logical Control Connection is to establish aconnection-based logical communication channel over the air between twobase stations that manage two DYSPAN (WRAN) systems respectively. Theidea of Over-the-air Logical Control Connections is based on thefollowing two key concepts: Bridge CPE and Coexistence Connections.

As shown in FIG. 13, a Bridge CPE (B-CPE) 1314 is located in theoverlapping coverage areas of two/multiple DYSPAN (WRAN) systems 1310and 1312, for which coexistence is required. Note that if there is noCPE located in the overlapping coverage areas of two/multiple DYSPAN(WRAN) systems, there should be no coexistence concerns. A B-CPE, as aregular CPE, associates with one of the base stations and establishesconnections for data transmission services, which are referred to hereinas Service Connections 1316. The associated base station for datatransmissions is called Service Base Station (S-BS) 1312 and theassociation is called Service Association. A Bridge CPE is selected byits service BS for coexistence communications. Requested by its serviceBS 1312, a bridge CPE 1314 associates with another base station, calledCoexistence Base Station (C-BS) 1310, with which the service BS requiresestablishing coexistence communications. The association between theBridge CPE 1314 and the Coexistence BS 1310 is referred to as acoexistence association. After it is associated with the Coexistence BS,the Bridge CPE 1314 establishes connections with the Coexistence BS, andthe established connections are called Coexistence Connections 1318 andare used only for coexistence communications. A Logical ControlConnection is established between the service BS and the coexistence BSover the service connection and the coexistence connection, with abridge CPE as the relay.

A coexistence connection 1318, as a regular connection in nature, is aconnection-based logical control channel that only carriescommunications for inter-system coexistence. A Coexistence Connection isestablished and maintained between a bridge CPE 1314 and a coexistenceBS 1310, when requested by the service BS of the bridge CPE. ACoexistence Connection can also be established and maintained betweentwo base stations when they are within range of each other, as shown inthe arrangement 1400 of FIG. 14. In this case, one of the base stations1410 behaves as a CPE of the other base station 1412.

A coexistence connection is established and maintained on physical RFchannels that are occupied by the coexistence BS 1310, 1410. No extraphysical RF channel is consumed for coexistence connections. Theestablishment and maintenance of a coexistence connection is performedalong with data transmissions of the bridge CPE 1314 (or service BS1412) controlled by the service BS 1312. The establishment andmaintenance of coexistence connections shall be in principle the same asthose for service connections, and shall include operations of ranging,connection acquisitions, and the like.

The service BS shall guarantee that the establishment and maintenanceoperations of coexistence connections are not co-scheduled with servicedata transmissions on the bridge CPE. The scheme for co-schedulingresolutions is described in the next section.

Over-the-air coexistence communications via LCC is established betweenthe service BS and the coexistence BS over the service connection andthe coexistence connection, with a bridge CPE as the relay.Functionalities of over-the-air coexistence communications are forcoexistence purpose only, and include messaging for on-demand spectrumcontention, sensing measurement sharing, transmission parameters (suchas frequencies, transmission power), and the like.

For a Bridge CPE with a single TX/RX front end, it shall be guaranteedthat service data transmissions are not co-scheduled (collided) withcoexistence operations (i.e. connection establishment and maintenance,control message exchange, etc.) on the Bridge CPE. For this matter, theService BS shall control and schedule the coexistence operations betweenthe Bridge CPE and the Coexistence BS. The scheduling scheme for servicedata transmissions and coexistence operations are depicted in FIG. 15.

Without being scheduled for coexistence operations by the Service BS1510, the Bridge CPE 1512 only maintains communications with the ServiceBS 1510 for service data transmissions 1520, 1522. Any coexistencemessages or scheduling 1532 transmitted from the Coexistence BS 1514 isignored by the Bridge CPE 1512. When being scheduled for coexistenceoperations 1524 by the service BS, the Bridge CPE requests 1534 andestablishes communications with the Coexistence BS for coexistenceoperations. The coexistence operations 1536, 1538 can be performed up tothe Coexistence Operation Period 1526 scheduled by the service BS. Afterthe Coexistence Operation Period expired, the Bridge CPE resumescommunications 1528, 1530 with the service BS and terminatescommunications 1540 with the coexistence BS.

Over-the-backhaul Logical Control Connections are now described. Asdescribed in the above section, when the coverage areas of multipleDYSPAN (WRAN) systems are overlapped, Over-the-air Logical ControlConnections using Bridge CPEs can resolve the inter-systemcommunications problems efficiently for coexistence. The inter-systemcommunications, however, may not be able to be established and/ormaintained using the Over-the-air Logical Control Connections in manycases, for which over-the-backhaul inter-system communications should beconsidered. FIG. 16 shows a scenario that favors over-the-backhaulinter-system communications instead of over-the-air LCC.

In this scenario, the coverage areas 1610 and 1612 of BS0 and BS1 arenot overlapped, and Over-the-air LCC is not able to be established andmaintained between BS0 1610 and BS1 1612, assuming a CPE (1616 or 1618)can only decode messages from base stations (1610 or 1612). These twoDYSPAN (WRAN) systems (1610 and 1612), however, require coexisting witheach other since, for example, CPE0 1616 associated with BS0 couldinterfere with CPE1 1618 associated with BS1 when they are operating onthe same channel.

To facilitate the over-the-backhaul communications between DYSPAN (WRAN)base stations, a management entity called “Coexistence ManagementEntity” (CoexistME) 1702 is used, which is located on top of the TCP/UDPlayer 1704 of each individual DYSPAN (WRAN) base station. A CoexistenceManagement Entity is used to manage message exchanges between the hostDYSPAN (802.22 WRAN) MAC and a remote DYSPAN (802.22 WRAN) MAC. TheCoexistME in the protocol stack 1700 is shown in FIG. 17. 802.22 MAC1712 transmits or receives coexistence messages to or from another802.22 MAC via the multi-layer management entity (MLME) 1716, CoExistME1702, TCP/UDP 1704, IP 1706 layers and the 802.3 MAC 1708 and 802.3 PHY1710 layers.

While there have been described above the principles of the presentinvention in conjunction with specific memory architectures and methodsof operation, it is to be clearly understood that the foregoingdescription is made only by way of example and not as a limitation tothe scope of the invention. Particularly, it is recognized that theteachings of the foregoing disclosure will suggest other modificationsto those persons skilled in the relevant art. Such modifications mayinvolve other features which are already known per se and which may beused instead of or in addition to features already described herein.Although claims have been formulated in this application to particularcombinations of features, it should be understood that the scope of thedisclosure herein also includes any novel feature or any novelcombination of features disclosed either explicitly or implicitly or anygeneralization or modification thereof which would be apparent topersons skilled in the relevant art, whether or not such relates to thesame invention as presently claimed in any claim and whether or not itmitigates any or all of the same technical problems as confronted by thepresent invention. The applicant hereby reserves the right to formulatenew claims to such features and/or combinations of such features duringthe prosecution of the present application or of any further applicationderived therefrom.

1. An RF sensing method comprising overlapping data transmissions withRF sensing to monitor a full spectrum of channels including those thatare in use for data transmissions, wherein bands of spectrum for RFsensing are adaptively selected to find a significant number of channelsthat are likely to be vacated while guaranteeing reliable and timely RFsensing performance and, after hopping to a new channel, a DYSPAN systemperforms data transmission on that channel for an operation period whichis terminated before the validation time of the channel plus the lengthof a grace period which is equivalent to the channel detection time. 2.The RF sensing method of claim 1 further comprising selectivelymonitoring the full spectrum of channels.
 3. The RF sensing method ofclaim 1 further comprising using at least one in-band channel for datatransmission.
 4. The RF sensing method of claim 1 further comprisingperforming RF sensing on selective out-of-band channels simultaneously.5. The RF sensing method of claim 1 further comprising specifying guardbands between in-band data transmission channels and out-of-bandspectrum sensing channels in order to mitigate adjacent interference. 6.The RF sensing method of claim 5 wherein the minimum width of the guardbands is variable.
 7. The RF sensing method of claim 1 wherein a numberof channels to be selected for RF sensing are adaptively adjustable. 8.The RF sensing method of claim 1 further comprising dynamicallyselecting and switching operating frequencies for data transmissions incontinuous time periods.
 9. The RF sensing method of claim 8 wherein thefrequency selection is based on simultaneous channel sensing performedalong with data transmissions.
 10. The RF sensing method of claim 8wherein both frequency selections and a length of an operation period ona selected channel are determined dynamically in real time by acognitive engine.
 11. The RF sensing method of claim 1 furthercomprising continuous operating periods having variable lengths.
 12. TheRF sensing method of claim 1 further comprising continuous operatingperiods having fixed lengths.
 13. The RF sensing method of claim 1wherein, except during an initial sensing period, a DYSPAN systemperforms both data transmissions on a working channel and RF sensing onchannels other than the working channel in operation spectrum, withguard bands separating the working channel and the channels beingsensed.
 14. The RF sensing method of claim 1 further comprisingselecting another channel in parallel with data transmissions, and atthe end of the operating period switching to the selected channel tobegin another continuous operating period.
 15. The RF sensing method ofclaim 1 further comprising a validation time of a channel defining theend of the sensing duration for that channel.
 16. The RF sensing methodof claim 1 further comprising a grace period defining a maximum periodof time in which a licensed incumbent service can tolerate interference.17. The RF sensing method of claim 1 further comprising performingcollision avoidance on multiple channels.
 18. An RF sensing methodcomprising overlapping data transmissions with RF sensing to monitor afull spectrum of channels including those that are in use for datatransmissions and dynamically selecting and switching operatingfrequencies for data transmissions in continuous time periods, whereinboth frequency selections and a length of an operation period on aselected channel are determined dynamically in real time by a cognitiveengine and, after hopping to a new channel, a DYSPAN system performsdata transmission on that channel for an operation period which isterminated before the validation time of the channel plus the length ofa grace period which is equivalent to the channel detection time.
 19. AnRF sensing method comprising overlapping data transmissions with RFsensing to monitor a full spectrum of channels including those that arein use for data transmissions and, after hopping to a new channel, aDYSPAN system performs data transmission on that channel for anoperation period which is terminated before the validation time of thechannel plus the length of a grace period which is equivalent to thechannel detection time.
 20. An RF sensing method comprising overlappingdata transmissions with RF sensing to monitor a full spectrum ofchannels including those that are in use for data transmissions, andfurther comprising a grace period defining a maximum period of time inwhich a licensed incumbent service can tolerate interference and, afterhopping to a new channel, a DYSPAN system performs data transmission onthat channel for an operation period which is terminated before thevalidation time of the channel plus the length of the grace period whichis equivalent to the channel detection time.